A team of 43 volunteers from 12 countries examined the list of references at the end of each chapter. We sorted these references into two groups -- articles published in peer-reviewed academic journals and other references. (Non-peer-reviewed material is often called "grey literature".) Then we calculated the percentage of references that do, indeed, appear to be peer-reviewed. . .

21 out of 44 chapters contain so few peer-reviewed references that the IPCC received an F. The IPCC relied on peer-reviewed literature less than 60 percent of the time in these chapters.